1. Field of the Invention
The invention relates to a method for verifying the calibration of a multi-port network analyzer and to a calibration unit.
2. Related Technology
Before implementing a measurement of the transmission and reflection coefficients of a device under test, vectorial network analyzers must first be calibrated. In this context, coefficient measurements, from which error terms are calculated, with which system corrections can be implemented in the actual measurement of the device under test, are carried out using three or more known, mutually-different calibration standards. For example, Open, Short, Match, or Through standards, which are connected in succession to the measurement ports, are used as calibration standards. It is already known, that these calibration standards can be formed, for example, on a substrate and arranged in the interior of a housing, from which respective cable connections project laterally. For the calibration, a calibration unit of this kind with calibration standards of fixed dimensions is connected via jacks and cables to the corresponding measurement ports of the network analyzer. The calibration procedure can then be implemented automatically under computer control.
It is also known from U.S. Pat. No. 5,578,932, that calibration standards of this kind can be realized as switchable complex impedances and that the various different calibration standards can be realized by switching.
After the calibration of the network analyzer has been completed, it is appropriate to implement a verification of the calibration. In practice, so-called T-checkers, which are connected to the measurement ports and with which corresponding coefficient measurements can then be implemented, are used for this purpose. For network analyzers with more than two measurement ports, the use of T-checkers of this kind is very awkward and susceptible to error because of the many screw connections required and the associated possibility of connection errors. In the case of two-port network analyzers using switchable impedances for the calibration, it is known from U.S. Pat. No. 5,578,932, that the same standards can be used for the verification as for the calibration. However, in this context, cabling errors (interchanged connections or faulty electrical connections at the jacks) cannot be detected, although these faults occur very frequently in practice. According to the known method, a complete verification is not possible, because the jacks are not detached during the transition from calibration to verification.